Incorrect Smooth object
To understand whats wrong you first need to understand what subdivider does.

Subdivider simply takes 3 vertices, and outputs the average of these 3 points, which in your case these are the points because your magazine lacks horizontal vertices
https://gyazo.com/a39bbb69b08b39541eac0cda3077ec60

you need to have vertical vertices along your magazine and other places where it deforms, something like this:
https://gyazo.com/4f41ac0fd74ee7850644daf9e7b975ed

and then add edge loops to sharpen corners.